Controversy exists as to whether the nephropathy in NIDDM is similar to that in IDDM, since the onset of NIDDM is difficult to ascertain. The NIDDK epidemiologic survey of Pima Indians provides a unique opportunity for the early detection of NIDDM and its associated nephropathy, a long- term follow up of both aspects of the disease, the opportunity to study their natural histories. However, there has been question as to whether the renal disease in the Pima resembles that in caucasians. Therefore, we studied autopsy kidney specimens from diabetic and control Pimas by morphometric techniques. The weighted mean of the area and a size-class distribution of the glomeruli were calculated with a computer-assisted planimeter in a series of autopsy kidney specimens of diabetic and non- diabetic Pima Indians. These morphometric variables were also related to the severity of histologic glomerular lesions, graded on a four class scale. Glomerular size did not differ in the two groups, nor were differences in the size distribution discernible among the classes of histologic lesions. A similar pattern was found in the Causcasian population affected by type-II DM. These data are in contrast to type I DM where there is an early increase in glomerular size followed by a late decrease in glomerular size as end-stage renal disease supervenes. Thus, the renal lesions in diabetic Pima indians resemble those in the caucasian population.